A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle of a user is equipped with a navigation function. Such a navigation system detects the position of the user or user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a hard disk. The navigation system displays a map image on a monitor screen while superimposing a mark representing the current location of the user on the map image.
When a destination is set, the navigation system starts a route guidance function for setting a guided route from the start point to the destination. To determine the guided route to the destination, the navigation system calculates and determines an optimum route to the destination based on various parameters. For example, the guided route is determined based on the shortest way to reach the destination, the quickest way to reach the destination, the route preferring freeways to surface roads, the least expensive way to the destination, the route without using toll road, or the like.
As new roads and buildings are constantly constructed, it becomes necessary to sometimes update the map data in the database of the navigation system so that it can accurately provide the most current information and guidance to the user. Moreover, it may also become necessary to upgrade the software and firmware of the navigation system as well for improving its performances. One method of updating/upgrading the navigation system is to allow only manufactures and authorized dealers to update the navigation system. However, this method has a problem of incurring higher cost and longer time because the user has to send the navigation system or the vehicle equipped with the navigation system to the manufacturer or dealer.
One way to update such data is to provide an update DVD or CD to copy the content of the optical medium into a rewritable media such as a hard disk drive of the navigation system. Nowadays, many vehicles have a DVD or CD entertainment system in combination with a navigation system. Thus, it is possible to provide a DVD or CD disk with updated data to a user of a navigation system so that the user can install the updated data in a hard disk of the navigation system through a CD/DVD driver of the entertainment system. This way of updating the map data or other data has the advantage of relatively low cost and short time in implementation.
However, the DVD or CD disk with the updated data can be sold or rent to others after the authorized user has installed the data in the hard disk of the navigation system. This is because once the data from the disk is installed, the operation of the navigation system does not depend on the presence of the disk. In other words, the user does not have to keep the disk after the installation. As a result, an unauthorized user may use those disks to install the updated data to their navigation systems.
To avoid such an act of unauthorized sale or copying of the updated data, an optical disk with a limited lifetime is proposed. In such an optical disk, because of the chemical action, the surface of the optical disk changes after unpacking within a certain amount of time, such as several hours or several ten hours, thereby disabling to copy the data. However, even if such an optical disk is used, it is possible to make illegal copying before the optical disk becomes unreadable.
Thus, there is a need to provide a navigation system that can prevent illegal copying while achieving a sufficient time to update the data for an authorized buyer with a relatively easy operation.